Production of carbide-surfaced wear-resistant ferrous bodies



3, 1954 s. J. SINDEBAND 2,685,545

PRODUCTION OF CARBIDE-SURFACED WEAR-RESISTANT FERROUS BODIES Filed Jan. 17. 1951 Patented Aug. 3, 1954 PRODUCTION OF CARBIDE-SURFACED WEAR-RESISTANT FERROUS BODIES Seymour J. Sindeband, Chappaqua, N. Y., as-

signor to Wearex Corporation,

Yonkers, N. Y.,

a corporation of New York Application January 17, 1951, Serial No. 206,382

3 Claims. 1

This invention relates to wear-resistant bodies or articles of the type having a ferrous or steel base provided on its exterior with a hard wearresistant continuous surface layer and to methods of producing such bodies.

Among the objects of the invention is a ferrous body or article provided with a wear-resistant continuous surface layer or casing consisting essentially of a carbide of at least one of the metals of the group consisting of titanium, columbium, tantalum, molybdenum and tungsten for use in applications requiring bodies or articles having exposed surfaces which are subject to wear.

A distinct object of the invention is a provision of a ferrous body or article provided with a wearresistant surface layer or casing consisting essentially of a carbide of at least one of the elements of the group consisting of titanium, columbium, tantalum, molybdenum and tungsten having a Vickers hardness of about 1500 to 1600 or higher.

A particular object of the inventionis a ferrous body or article provided with such wear-resistant carbide surface layer on only certain surface portions thereof, with other surface portions of the article being free from such carbide surface layers.

According to the invention, a ferrous body or article having at least in the surface layer thereof at least about 0.4 percent available carbon is provided with a wear-resistant continuous surface layer of a metal carbide having a Vickers hardness of at least about 1500 to 1600, by causing at least one of the metals of the above specified group to be. deposited at an elevated temperature on the surface of the body-and cause the deposited metal to diffuse into the surface layer of the ferrous body and to combine with the carbon content thereof to produce a wear-resistant carbide surface layer of a thickness of at least about 8 microns having such high hardness.

As used herein in the specification and claims, Vickers hardness means hardness in numbers determined by Vickers diamond pyramid hardness tests, such as described for instance in the Metals Handbook, 1939 edition, published by the American Society for Metals.

The foregoing and other objects of the invention will be best understood from the following description of eXemplifica-tions thereof, reference being had to the accompanying drawings wherein:

Fig. 1 is anelevational view of a conventional thread guide having a wear-resistant carbide casing of the invention, and

Fi 2 is a cross-sectional view of a ball bearing having wear-resistant carbide surface regions of the invention.

For years past ferrous bodies or articles with hard wear-resistant surfaces have found many applications in the arts as for example the moving parts of machinery subject to Wear and shock. Heretofore, it has been generally believed that the most satisfactory wear-resistant hard surface for a ferrous article is that provided by electrodeposition of a layer of chromium from an electrodeposition bath on'the surface of the body. However, such chromium surface layer, even if formed under the most favorable conditions, exhibits at mostabout 800 Vickers hardness and ha only a limited wear-resistance.

The present invention is based on the discovery that under certain critical conditions of a carbon content of the ferrous body and the thickness of its cross-sectional area it is possible to provide the entire or only a, limited exposed surface region of such body with a wear-resistant titanium carbide layer forming an integral part of the body and exhibiting a Vickers hardness of 1500 to 1600 or even more, thus multiplying the life of such wear-resistant bodies or articles compared to the prior art chromium coated wear-resistant bodies.

In accordance with the invention a ferrous or steel body containing at least 0.4% carbon having a certain minimum thickness in relation to its carbon content will, when subjected at an elevated temperature to a surface alloying action in which titanium is deposited on the surface of the body, cause the deposited titanium to diffuse into the surface layer of the body and combine with carbon migrating from the interior to form a titanium carbide surface layer which permits continued deposition of titanium on the exterior surface of the body, the additional deposited titanium continuing to combine with the carbon in the surface layer until a titanium carbide surface layer of a thickness of at least about 8 to 16 microns having at least about 1500 Vickers hardness has been formed on the surface of the body as an integral part thereof.

Important factors affecting the nature of a titanium carbide casing formed on the surface of a ferrous article are the percentage of its carbon content, the thickness of the ferrous body in relation to its total carbon content, and the percentage of alloying elements having a greater afiinity for carbon than titanium. The ferrous or steel article should have an available carbon content of at least 0.4% and should be of substantial thickness of at least about .020 inch so that carbon of the interior can diffuse from relatively deep areas below the surface to combine with titanium deposited on the surface of the article at an elevated temperature from a gaseous or liquid titanium compound into a wear-resistant titanium carbide surface layer ofv substantial thickness. Highly satisfactory titanium carbide surface layers will form on ferrous articles containing 0.60 to 1.20% carbon.

A feature of the invention is the discovery thatfor a ferrous body having. a carbon content of at least 0.4% and a certain minimum thicknessthe titanium carbide casing formed on its exterior by the treatment of the invention will increase in hardness as the thickness of the ferrous body increases. until it. reaches a. maximum hardness which does not increase with a further increase in thickness of the ferrous body. The increase of the hardness of the titanium carbide casing caused by the increase u in. the thickness of the ferrous. body shows that titanium of greater carbon content and greater hardness and formed on ferrous bodies. having a certain mimmum thicknessv than in ferrous bodies of lesser thickness. In other words, in. order to form on a ferrous body containing at least (L V/"a carbon a titanium carbide casing having a minimum of 15% to 1500 Vickers hardness, the ferrous body must have a minimum thickness of at least about .920 inch so that the carbon from the interior may diffuse into the surface layer of the body onwhich the titanium is deposited to provide the additional carbon required for causing the deposited. titanium to combine with the carbon of the body into a titanium carbide layer of a minimum of atv least about. 15cc to 1689 Vickers hardness.

There are indications that the hardness of titanium carbides increases with the increase of the carbon content of the carbide. Furthermore, there are indications that the hard carbide surface layer or casing of the invention of a thickness of at least about 8 microns. and of at least 1500 Vickers contains or consists, at least to some extent, of a multiple carbide. containing carbon combined with the deposited titanium and with iron of the base or article.

As used herein. in the specification and claims the expression metal carbide surface layer and metal carbide casing are intended to mean a 7.

metal carbide surface layer or casing consisting essentially either of a carbide of the deposited metal or of a multiple carbide of the deposited metal and of iron. from the article base or of a mixtureor combination of carbides. This applies to carbide casings of the invention usin as a carbide-forming coating metal, at. least one of the metals of the group consisting of titanium, columbium, tantalum. molybdenum and tungsten.

When forming on the exterior of a ferrous body a titanium carbide casing of the invention, the interior of the ferrous body or its core. is. depleted of carbon or decarburised. If such ferrous body is thin and has been depleted of its carbon content by the formation of a titanium carbide casing on its exterior, the decarb-urized core of such body will lose its ability to be hardened through subsequent heat treatments of the type generallyused for hardening steel bodies.

According to the invention, ferrous articles which are to be provided with a titanium carbide casing of the invention are chosen to contain sufficient carbon and be of sufficient thicknessv so that-after forming on the exterior of the body the titanium carbide casing of a minimum thickness of at least 8 microns and at least 1500 to 1600 Vickers hardnessthe ferrous core of the body will retain a carbon content of at least 0. so that it may be subjected to known heat treatments by which similar carbon-containing steel bodies are hardened. It. is thus possibleto provide ferrous bodies with a wear-resistant titanium carbide casing of the invention, which may be subjected to known heat treatment whereby the. ferrous articies are given enhanced strength as well as other desired characteristics.

among: the various: ferrous articles whose surfaces have been provided with a wear-resistant continucuisv surface layer of titanium carbide in accordance with this invention are thread guides, cylinders, pistons, dies, drills, cutters, ball and roller bearings with associated races, phonograph needles, etc. In general, the invention may be applied tov any ferrous article having a surface which is subjected to wear.

Any of the known. methods for depositing titanium from a. gaseous or liquid titanium compound on the surface of a ferrous body heated to. an elevated temperature. below the melting temperature of the body may be employed for depositing titanium on and diffusing titanium into the surface layer of. the ferrous. body to combine with carbon and for forming. a wear-resistant surface layer of titanium carbide.

These methods include chemical reduction or reaction of the titanium compound. at the surface of the ferrous article as exemplified by hydrogen reduction of titanium halides and by displace ment or reaction of the ferrous base metal with one of the constituents of the titanium compound. Another method that may be used for depositing titanium on and diffusing titanium into the surface layer of the ferrous body to combine with carbon and for forming a. wear-resist ant surface layer of titanium compound is thermal decomposition of a. titanium compound atthe surface of the ferrous article as exemplified by thermal decomposition of titanium. halides at the surface of the ferrous article at high temperatures and by thermal decomposition of titanium carbonyl at the surface of the ferrous. artiole at low temperatures- According to the invention, it is also possible to provide ferrous bodies or articles which have a low carbon content with a. wear-resistant titanium carbide layer by first forming on the surface thereof, by a known carburizing process, a carburized surface layer or casing of high carbon content, and thereafter subjecting the so carburized surface region to the titanium depositionand titanium-carbide-casing forming treatment.

When producing titanium carbide casing on a smoothly ground polished or other mechanically worked surface of a ferrous article, surface im perfections arranged in a fashion suggesting scratches, tool marks, grinding marks, machining patterns; and/or welts-will appear on the exterior surface of the titanium carbide layer. The formation of these protuberances and \velts appears to occur to a lesser extent in low carbon steels. It seems that such protuberant swellings or growths appear at portions of the titanium carbide surface layer formed on worked or Work-affected surface portions of the ferrous base. As used herein in the specifications and the claims, the expression work-affected surface portions means. surface portions of a ferrous article the material of which was worked. upon as by grinding, polishing, rolling, etc., thereby giving its sur face structure a characteristic distinct from underlying portions with respect to the tendency to form the titanium carbide surface layer of the invention. It has been observed that the titanium carbide surface layer of the invention, when formed on work-affected surfaces of a ferrous article, exhibits such objectionable surface irregularities even when the article is subjected to a heating or annealing treatment in the initial stages of or prior to the titanium-carbide casing forming process.

According to another phase of the invention, the objectionable surface irregularities of the wear-resistant titanium carbide layer are eliminated, prevented or suppressed by removing the work-affected exterior surface stratum of the article before treating the article to form thereon the titanium carbide surface layer. Any known processes, such as etching, deplating and the like which are effective in removing a surface stratum from the exterior of a ferrous body without forming a new surface of the same kind, may be used for removing the work-affected surface layer of the article so as to suppress surface irregularities on the titanium carbide layer formed on the exterior of the ferrous article.

By way of example, the work-affected surface stratum of the ferrous article may be removed by treating the surface with a solution of HCl containing 50% by volume concentrated hydrochloric acid HCl, balance water, while heated at about 85 C. for 2 to minutes. Other known etching compounds may be used for removing the work-affected surface layer from the surface portions of the article which are to be provided with the titanium carbide wear-resistant surface layer. Alternatively, the ferrous article which has a work-affected surface may be placed in an electrolyte bath of suitable concentration and connected as anode in an electrodeposition circuit for removing'the work-affected surface layer by the electrodeposition process. Any known electrolytic deposition baths may be'used for this purpose such as HCl solution. V

For most practical applications good results are obtained with wear-resistant ferrous or steel articles provided in accordance with the, invention, witha wear-resistant surface layer of titanium carbide having a thickness of about 12 to 18 microns and up to about 25 microns or 4 of an inch, although in some applications it may be desirable to provide ferrous articles with wearresistant titanium carbide surface layers of a thickness greater than about 25 microns.

It is possible, according to'the invention, to provide only those surface portions of the ferrous article exposed to wear with-the wear-resistant titanium carbide casing. Thus, in case of the thread guide shown in Fig. 1, the spirally shaped upper guide portion is provided with the titanium carbide surfaced layer and its threaded lower portion M is left untreated and without the carbide layer. Similarly, in case of the ballbearing shown in Fig. 2, only the spherical surface of the balls and the race surfaces Hiof the ball races I! and I8 are provided with the titanium carbide layer of the invention.

Such partial titanium carbide casing may be formed by providing those surfaces on which formation of the carbide-layer is to be prevented or suppressed with a stop coating or stop cover which prevents deposition of titanium on its surface while titanium is deposited on the weara bath formed of a ing surfaces of the article to provide the desired titanium carbide casing or layer. Such stop coating may consist of a coating of metal such as copper which is lower in the electromotive series than titanium.

In a similar manner, exposed surfaces of a ferrous article of low carbon content o n which formation of a carburized layer is to be "pi'evented or suppressed-are provided with a similar stop coating or stop cover which effectively pre-" vents deposition of carbon on its surface with carbon is deposited by a carburizing action on the wearing surface of the article for producing thereon a'surface layer of high carbon content;

By way of example, in case of the thread guide of Fig. 1, a copper stop coating is formed only on the threaded lower portion M. In case of the bearing of Fig.2, a copperstop coating is formed on all surfaces of the ball races l1, l8 except the two race surfaces [6.

As explained above, the ferrous article 'must have atleast about 0.4 to 0.6% available carbon" content, and a certain minimum thickness of 'at' least about .020 inch so that the carbon diffusing from relatively deep regions below the surface may combine with the titanium deposited at the surface for producing thereon a titanium carbide casing having a thickness of at least about 8' microns and at least about 1500 to 1600 'Vic'kers hardness. The critical relationship betweenthe carbon content of the ferrous body and its tl'ii'ck ness to the character of the titanium carbide layer-of the invention formed thereon can'be shown by treating wedges of known 'carbon'content to form on the exterior of the wedges a titanium carbide casing of the invention in' the way analogous to that described in my copending application Ser. No. 206,380 filed January 1'7, 1951, in connection with Fig. 4 thereof. In the thin tip region of such edge, the deposited titanium will diffuse and become alloyed with the ferrous particles of the body, and it will have only negligible titanium carbide content. Such thir'r wedge tip remains relatively soft and has the characteristics of titanium alloyed iron.

The adjacent somewhat thicker region of such wedge will have on its exterior'a thin stratum of titanium carbide overlying a relatively thick layer of titanium alloyed iron'formed over an inner ferrous core which is substantially free of" carbon, all the carbon having migrated to the surface to form with the deposited titanium the thin titanium carbide stratum. In the still thicker region of such wedge the titanium de' posited on the surface willhave combined with the carbon that migrated from its interior into: a titanium carbide surface layer overlyinggthe ferrous core which is substantially free from carbon. A still thicker region of the wedge will have on its exterior a titanium carbide surface layer overlying a core containing, in addition'to a ferrous particle free from carbon, carbon con-' taining pearlite formations. Such wedge 'will thus have a cross-sectional region of a thickness in which the first pearlite colonies appear, the core of the wedge becoming richer in pearlite content asits cross-section increases. Only the Wedge portions rich in pearlite will retain'the ability of becoming hardened by known steelhardening heat treatments.

It can also be shown that the hardness of the carbide surface layer formed on such wedge increases until it reaches a maximum of about 1500' to 1800 Vickers hardness for certain thickness or the carbon containing ferrous wedge and-the the carburized exterior the desired carbide casing.

As explained hereinbefore, after producing the carbide surfaced ferrous articles in which the core retains enough carbon to have a pearlite structure, they may be subjected to further heat treatment of the type applied to steel for imparting thereto high mechanical strength such as required by drills, cutters, and like articles. Such further heat treatment may be readily carried out without affecting the carbide surface casing previously formed on the article.

The principles of the invention described above in connection with specific exemplificaticns thereof, will suggest various other modifications and applications of the same. It is accordingly desired that the present invention shall not be limited to the specific exemplifications shown as described above.

I claim:

1. In the method of making articles having an exposed wear-resistant surface region consisting essentially of a metal carbide forming an integral part of said article and constituting only a small fraction of the mass of said article, the procedure comprising the steps of providing a ferrous body having a mechanically worked surface on a portion thereof that is at least 0.020 inch thick and containing adjacent the surface thereof at least 0.4% of available carbon, removing the stratum of wcrk-aifected ferrous surface particles from said surface region, depositing at an elevated temperature, on the exposed surface region of said body at least one metal selected from the group consisting of titanium, columbium, tantalum, molybdenum, and tungsten from a compound of said metal and causing the deposited metal to react with available carbon of said surface region to produce out of an integral surface layer of said surface region of said article a metal carbide layer consisting essentially of a carbide containing said deposited metal, and continuing said deposition of said metal and the carbide forming reaction of the so deposited metal with the available carbon of said surface region until an integral layer of said metal carbide at least about 8 microns thick having a surface hardness of at least about 1500 Vickers hardness is integrally formed on said surface region.

2. The method of claim 1 in which a portion of the exposed surface of the ferrous article is provided with a coating to prevent the formation of metal carbide thereon prior to the deposition of the carbide forming metal.

3. The method of claim '1 in which the metal deposited is titanium.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN THE METHOD OF MAKING ARTICLES HAVING AN EXPOSED WEAR-RESISTANT SURFACE REGION CONSISTING ESSENTIALLY OF A METAL CARBIDE FORMING AN INTEGRAL PART OF SAID ARTICLE AND CONSTITUTING ONLY A SMALL FRACTION OF THE MASS OF SAID ARTICLE, THE PROCEDURE COMPRISING THE STEPS OF PROVIDING A FERROUS BODY HAVING A MECHANCIALLY WORKED SURFACE ON A PORTION THEREOF THAT IS AT LEAST 0.020 INCH THICK AND CONTAINING ADJACENT THE SURFACE THEREOF AT LEAST 0.4% OF AVAILABLE CARBON, REMOVING THE STRATUM OF WORK-AFFECTED FERROUS SURFACE PARTICLES FROM SAID SURFACE REGION, DEPOSITING AT AN ELEVATED TEMPERATURE, ON THE EXPOSED SURFACE REGION OF SAID BODY AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM, COLUMBIUM, TANTALUM, MOLYBDENUM, AND TANGSTEN FROM A COMPOUND OF SAID METAL AND CAUSING THE DEPOSITED METAL TO REACT WITH AVAILABLE CARBON OF SAID SURFACE REGION TO PRODUCE OUT OF AN INTEGRAL SURFACE LAYER OF SAID SURFACE REGION OF SAID PARTICLE A METAL CARBIDE LAYER CONSISTING ESSENTIALLY OF A CARBIDE CONTAINING AND DEPOSITED METAL, AND CONTINUING SAID DEPOSITION OF SAID METAL AND THE CARBIDE FORMING REACTION OF THE SO DEPOSITED METAL WITH THE AVAILABLE CARBON OF SAID SURFACE REGION UNTIL AN INTEGRAL LAYER OF SAID METAL CARBIDE AT LEAST ABOUT 8 MICRONS THICK HAVING A SURFACE HARDNESS OF AT LEAST ABOUT 1500 VICKERS HARDNESS IS INTEGRALLY FORMED ON SAID SURFACE REGION. 